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    5W30 vs 5W40 in a GM car

    As a 30 Mercedes veteran technician, I find it strange that GM insists on a 30 weight oil, whether a 5W30 or 10W30. These are the only oils recommended in the manual. Where Mercedes, with bearing clearances just as tight allows a full range of viscosities of oil ranging from 0W30 to 20W50...